Conventionally, rotating electrical machines are known which include concentric coils of the same phase connected in parallel with each other.
A plurality of concentric coils (e.g., first to fourth round wire concentric coils) formed by concentrically winding a round wire and connected in parallel with each other are conventionally known in the art. Each of the first to fourth round wire concentric coils includes a plurality of coils (hereinafter referred to as the coil portions) connected in series with each other. The first to fourth round wire concentric coils are placed in slots of a stator core in order of the plurality of coil portions of the first round wire concentric coil, the plurality of coil portions of the second round wire concentric coil, the plurality of coil portions of the third round wire concentric coil, and the plurality of coil portions of the fourth round wire concentric coil (namely, the coils are wound around adjacent poles).
For example, in the case where the central axis of a rotor is not aligned with the central axis of a stator, the positional relationship between each permanent magnet placed in the rotor and each of the first to fourth round wire concentric coils may be imbalanced. In this case, a circulating current flows in the concentric coil, which results in generation of noise and vibration, etc.
In order to overcome this disadvantage, one of the coil portions of the first round wire concentric coil, one of the coil portions of the second round wire concentric coil, one of the coil portions of the third round wire concentric coil, and one of the coil portions of the fourth round wire concentric coil are conventionally placed in this order in the slots of the stator core (namely, the coils are wound around every other pole). This eliminates the imbalance in the positional relationship between each permanent magnet and each of the first to fourth round wire concentric coils and thus reduces generation of noise and vibration due to a circulating current in the concentric coil.
Conventionally, rotating electrical machines are also known which include a concentric coil formed by concentrically winding a rectangular wire. Such a rotating electrical machine is disclosed in, e.g., Japanese Patent Application Publication No. 2012-125043 (JP 2012-125043 A).
JP 2012-125043 A discloses a motor including a first concentric coil and a second concentric coil which are formed by concentrically winding a rectangular wire. The first concentric coil is formed by winding a rectangular wire so as to create a clearance between adjacent ones of the turns of the rectangular wire so that the rectangular wire of the second concentric coil can be inserted in the clearances. That is, in JP 2012-125043 A, portions of the rectangular wire of the first concentric coil and portions of the rectangular wire of the second concentric coil are alternately placed in each slot of a stator core in the radial direction of the stator core.